18. Card blocks and volumes

A CP/M disk read transfers 128 bytes. An SD card read transfers 512 bytes. The BIOS joins these two sizes by mapping each CP/M record to a quarter of a card block. The volume's start block supplies the other part of the address so the same track and sector can name different card blocks on A and B (src/bios.asm:5-11, src/bios.asm:128-185).

The eight disk entries in the BIOS are HOME, SELDSK, SETTRK, SETSEC, SETDMA, READ, WRITE and SECTRAN. They separate the BDOS's record operations from the card's electrical interface. A volume descriptor defines the permitted range between those boundaries. The block cache holds the 512-byte blocks used for both record transfers and container-table reads (src/tables.asm:23-31, src/cache.asm:173-201, src/vol.asm:378-416).

Bytes on the card interface

The TEC-1G's SD adaptor uses port FDh. Output bit 0 is MOSI, the data sent to the card. Bit 1 is the clock and bit 2 is active-low chip select. Input bit 7 is MISO, the data received from the card. The driver changes outgoing data with the clock low and supplies a rising edge for the card to sample it (src/layout.asm:15-20, src/sd.asm:1-7, src/sd.asm:35-69).

SPIW sends a byte from its top bit down. Each pass shifts the next bit from C into carry and writes it with the clock low then high. SPIR receives a byte with MOSI held high. It clocks each bit and shifts the sampled input bit into the result. SPIEND raises chip select and supplies eight more clocks while preserving the result of the preceding operation (src/sd.asm:35-89).

SDCMD first sends an idle FFh then a six-byte command. The first byte is the command number with bit 6 set. Four argument bytes follow from SDARG most significant first. A CRC byte ends the command. The driver supplies 95h for CMD0, 87h for CMD8 with argument 1AAh and 01h for other commands. In the default SPI CRC mode only CMD0 and CMD8 need valid CRC bytes. The other commands get the end bit alone. SDCMD reads at most sixteen bytes for R1, the response whose bit 7 is clear (src/sd.asm:100-143).

The high-level operations SDINIT, SDREAD and SDWRITE return Z with A and SDERR zero on success. Failure returns NZ with the error code in both places. This contract does not describe the raw byte-transfer helpers or LBAARG, whose range failure uses carry (src/sd.asm:334-387, src/sd.asm:397-457, src/sd.asm:667-737).

Initialisation and block addresses

SDINIT establishes whether later commands need block or byte addresses. It starts with SDBYTE clear and performs these steps (src/sd.asm:190-351):

1. Supply 80 clocks with chip select high, exceeding the power-up minimum of 74, then send CMD0. R1 must be 01h, the idle state. Each of up to ten attempts includes those clocks. Exhaustion returns error 1, SDENOCD, also the usual empty-socket result.
2. Send CMD8 with argument 1AAh. Only R1 = 01h enters the four-byte echo check. The third byte's low nibble must be 1 for the 2.7–3.6 V range and the fourth byte must be AAh. A mismatch returns 0Bh, SDEVOLT. Any other R1 skips this check. That branch accommodates older cards which reject CMD8, though the code does not restrict it to an illegal-command response.
3. Send CMD55 followed by ACMD41 with HCS, bit 30, set. R1 = 0 from ACMD41 ends the loop. Otherwise the driver makes up to 256 attempts with a short 256-turn pause between them. A CMD55 response with any bit except idle bit 0 set returns error 2, SDEINIT, immediately and sends no ACMD41. Exhausting the attempts gives the same error.
4. Send CMD58 and require R1 = 0, otherwise return error 3, SDEOCR. Read the four-byte operating conditions register. CCS, bit 6 of its first byte, selects block addressing when set.
5. With CCS clear set SDBYTE to 1 and send CMD16 to set a 512-byte block length. Failure returns error 4, SDEBLEN.

Every subsequent access supplies a four-byte block number in SDLBA, least significant byte first. LBAARG writes its big-endian command argument to SDARG. A high-capacity card gets the block number unchanged. A standard-capacity card gets the block number multiplied by 512 because its commands use byte addresses (src/sd.asm:354-387).

The multiplication must fit in 32 bits. 7FFFFFh is the last addressable block in that mode and becomes byte address FFFFFE00h. A block number of 800000h or more would overflow. LBAARG returns carry before changing SDARG in that case. Both transfer routines return error 9, SDERNG, before sending a card command. This is the byte-addressing ceiling at 4 GiB, not a measurement of the inserted card's capacity (src/sd.asm:354-387, src/sd.asm:397-400, src/sd.asm:454-457, src/sd.asm:667-670).

Reading and writing a block

SDREAD sends CMD17. A nonzero R1 returns error 5, SDECMD. After a successful response it polls for the data token. FFh means continue waiting and FEh starts the block. The wait permits 65,536 polls before error 6, SDETOK. Every other byte ends the read immediately with error 0Ah, SDEDTOK. This includes the card's 000xxxxx data-error tokens. After FEh the driver receives 512 data bytes and reads the two CRC bytes without checking them (src/sd.asm:397-457).

The extra error-token classification costs 11 T-states on a normal FFh wait: INC A followed by the untaken JR NZ,SDRERR. That is only the additional check, not the entire token poll (src/sd.asm:421-422). The retired diagnostics ROM's account at b706f61:docs/diagnostics.md:285-291 gives 678 T-states for a full poll in that ROM. The 11-T-state addition therefore cannot be compared directly with that full-poll cost.

SDWRITE sends CMD24 and also requires R1 = 0 or returns error 5. It sends an idle byte, FEh, the 512-byte block and two FFh CRC bytes. It reads up to sixteen bytes for a non-FFh response. The low five bits must be 05h for data accepted. Any other response or no response returns error 7, SDEWRSP. The busy wait then permits 65,536 reads of 00h. Any nonzero byte ends that wait successfully. Exhaustion returns error 8, SDEBUSY. Success therefore follows the end of reported busy, not merely acceptance of the data token (src/sd.asm:667-737).

Both block-transfer loops have the eight bit operations written out for each byte. SDRBLK counts 256 two-byte passes in the Z80's I register. That register supplies no interrupt-vector address in this ROM's interrupt mode 1 (src/boot.asm:35-40). SDWBLK uses two passes of 256 bytes. These routines clobber their declared registers, including I on the read path (src/sd.asm:459-655). On the host model SDREAD takes 219,232 T-states per block (about 55 ms at 4 MHz) and SDWRITE takes 216,264. Most of that work transferred the block's 4,096 bits individually.

A cache transfer sets SDXB to LATEXP. The block loop then selects EXPAND 1 for the buffer and restores LATCHV before returning. It uses no stack while EXPAND 1 is visible (src/cache.asm:183-195, src/cache.asm:213-237, src/sd.asm:469-478, src/sd.asm:566-591, src/sd.asm:646-655). The BIOS transfer paths and descriptor-service cache walks disable maskable interrupts around their work. The SD transfer itself does not supply a general interrupt guard. The reason for this boundary is the EXPAND 1 stack rule (src/bios.asm:395-399, src/bios.asm:418-422, src/vol.asm:535-545). Appendix D relates the SD error codes to likely causes and recovery.

Container blocks and validation

TEC-OS uses a single container on the card. It describes which ranges are volumes. Block 0 starts with TECOSVOL, the major and minor versions, header and descriptor sizes, volume count, container length in blocks and a checksum. Format 1.1 adds a drives field and an extra-table sum. The descriptors are 32 bytes each. Fifteen fit after the header fields in block 0 and sixteen fit in each of blocks 1–7, for a maximum of 127 (format/format.json:2-42).

The ROM's field offsets and geometry definitions are generated from format/format.json into gen/format.asm and gen/geom.asm (tools/build.mjs:79-134). Appendix E contains the byte layout and the host/ROM validation comparison. A fresh table read avoids using bytes cached during an earlier mount.

MNBLK obtains a cache line for the requested table block. MNTCB records the table block last read for this operation. A different block forces a card read even on a cache hit. Cold MOUNT and service entry VSIN set MNTCB to FFh, forcing the first read too (src/vol.asm:42-48, src/vol.asm:378-421, src/volsvc.asm:353-357).

Obtaining a line can first require writing a dirty victim. CWRITE restores SDLBA by remapping the BIOS record after that write. MNBLK therefore calls MNLBA again before filling the line, restoring the requested table block's address. A failed eviction or read ends this operation with NZ (src/cache.asm:213-251, src/vol.asm:399-435). MNCPH copies 32 bytes through MVCOPY into the resident workspace's MNBUF. Field checks and sums then use ordinary workspace memory. MNSUM processes a whole block in these 32-byte pieces without stack use under the EXPAND 1 mapping (src/vol.asm:438-501, src/ram.asm:108).

MOUNT initially empties all drives. It checks the header in this order and returns the first failing check's hexadecimal code (src/vol.asm:11-30, src/vol.asm:42-143):

Check	Failure
Block 0 can be read	20h
The eight magic bytes are TECOSVOL	21h
Major version is 1	22h
Header size is 512 and descriptor size is 32	23h
Volume count is 1–8 for minor 0, otherwise 1–127	24h
Header checksum equals the 16-bit sum of the other 510 bytes	25h
For a nonzero minor version, drives is 0–4	23h

Minor 0 selects the format 1.0 path. Every other minor value selects the 1.1-style checks, not only minor 1. The host creator uses 1.1 for more than eight volumes or a nonzero drives field (src/vol.asm:89-100, src/vol.asm:132-143, tools/lib/container.mjs:79-85).

For that path, the number of table blocks after block 0 is floor(volumeCount / 16). MOUNT adds every byte of those whole 512-byte blocks, including unused descriptor bytes, modulo 65,536. An unreadable block returns 20h and a mismatched sum returns 25h. There is an exact exception: with fifteen or fewer descriptors, the zero-block branch skips the comparison altogether. The ROM accepts a nonzero stored tableSum there if the other checks pass. The host parser computes an empty sum of zero and rejects a nonzero stored value (src/vol.asm:145-180, src/vol.asm:479-501, tools/lib/container.mjs:41-49, tools/lib/container.mjs:127-145). HDRSUM uses the same byte-summing path for block 0 and subtracts its two checksum bytes before comparison (src/volutil.asm:83-128).

The descriptor walk validates each descriptor then installs its assigned drive before advancing. A later failure calls UNMOUNT so the returned result is all mounted or all empty (src/vol.asm:182-201, src/vol.asm:325-365).

A descriptor check returns 26h for a zero volume id, unsupported flag bits, an unknown geometry, the wrong payload length or an invalid start. Only the read-only flag bit is allowed. Length must equal the geometry's payload, with its upper word zero. The start must be nonzero and a multiple of eight blocks. These checks place every payload at block 8 or later (src/vol.asm:204-244).

The walk compares the start against the previous volume's exclusive end. A lower start returns 28h. It then computes end = start + length in 32 bits. Carry out or an end above containerBlocks returns 27h. Ascending descriptor order therefore prevents overlapping payloads. The exclusive end is the first block after the volume. On a standard-capacity card it may equal 00800000h, giving last block 007FFFFFh. An end above 00800000h is rejected. High-capacity addressing has no such byte-address limit (src/vol.asm:245-296).

The drive field is FFh for unmounted or 0–3 for A–D. A nonzero header drives count also bounds the assigned drive. Assigning a drive twice returns 29h. After the walk, an empty A returns 2Ah (src/vol.asm:307-353). The ROM checks that ids are nonzero but does not check their uniqueness. It interprets only bit 0 of the separate cache byte as written-behind and ignores its upper bits (src/vol.asm:204-211, src/vol.asm:582-598).

The host validator also checks cache flags and duplicate ids. For nonzero minor versions it checks duplicate labels too. By default it compares the declared extent against the image's byte length. Its checks and the ROM's checks are not universally nested. The host parser has no SDBYTE card-mode input for the standard-capacity limit. Neither path validates every reserved byte. Appendix E gives the field-by-field boundary (tools/lib/container.mjs:127-185, src/vol.asm:204-353).

Declared length and physical capacity

MOUNT checks against the declared container length. It reads no card CSD to establish physical capacity. A payload can therefore pass validation yet extend beyond the real card or model image. Later failure depends on the card's response. A nonzero R1 from CMD17 gives SD error 5 and a failed BIOS read reaches the BDOS's Bad Sector path (src/vol.asm:254-296, src/sd.asm:397-405, src/sd.asm:445-446, src/cpm/bdoslog.asm:89-107, src/cpm/bdoscon.asm:23-74).

The source assertions in test/sd-range.test.mjs:36-106 cover two distinct bounds. A standard-capacity volume starting at 800800h or straddling the limit from 7FF000h is rejected with 27h. A volume ending exactly at 800000h mounts, as does the straddling volume in high-capacity mode. The beyond-image cases assert error 5 without image changes. These are statements about the recorded test cases, not newly executed results.

The short-image capture uses a copy of dist/starter.img truncated with truncate -s 2105344 build/short.img. Its first 4,112 blocks include only sixteen of B's thirty-two directory blocks. Logging B in reaches the missing seventeenth block. After the error, A's directory remains accessible:

TEC-OS 0.1 for TEC-1G
A: SYSTEM
B: WORK
C: PROJECTS

A>SHELL.SVC

A:SYSTEM>GLCD.SVC

A:SYSTEM>DIR B:

Bdos Err On B: Bad Sector
A:SYSTEM>DIR A:*.CMD

STARTUP .CMD     128
1 file, 128 bytes
935936 free on A:SYSTEM
A:SYSTEM>

A header failure takes a different route. Cold boot enters the diagnostic prompt after either SDINIT or MOUNT fails (src/boot.asm:97-101). The following capture uses another starter-image copy with its first T changed to X by printf X | dd of=build/bad.img bs=1 seek=0 conv=notrunc. Typing H produced another prompt:

TEC-OS 0.1 for TEC-1G
No volume mounted, error 21
R retry> H
R retry>

21h is MEMAGIC. R or r retries card initialisation and mounting. Any other key repeats the prompt (src/vol.asm:13-14, src/boot.asm:646-667). Appendix E includes host-side header inspection.

Drive entries and disk parameters

A successful descriptor install builds two related structures. The BIOS uses an eight-byte entry in DRVTAB: four bytes of start block, two of length, one of geometry and one of flags. MNFILL copies the contiguous start and low length fields with one LDIR. Read-only occupies flag bit 0 and written-behind occupies bit 1. DRVIDX separately holds container index plus one, with zero for an empty drive (src/vol.asm:558-598, src/ram.asm:37-55).

An empty entry has geometry zero. SELDSK returns HL = 0 for that drive or a number past D and leaves DSKCUR unchanged. For a valid drive it sets DSKCUR and returns its disk parameter header (DPH). DPHADR computes DPHTAB + 16 × drive (src/bios.asm:53-92). MNDPH fills the sixteen bytes as follows (src/vol.asm:600-636, src/ram.asm:71):

Offset	Contents
0	Zero sector-translation pointer, meaning no skew
2–7	Three BDOS scratch words, initially zero
8	Shared 128-byte DIRBUF
10	Pointer to the geometry's disk parameter block (DPB)
12	CSVDUM, unused because CKS is zero
14	Allocation-vector pointer set by ALVINIT, left intact by MNDPH

The two geometries use 64 records per track, no reserved tracks and four allocation blocks for the directory. Their sizes are (format/format.json:46-58, tools/lib/format.mjs:9-40):

Parameter	G8M (DPB1)	G1M (DPB2)
Geometry id	1	2
Payload in SD blocks	16,384	2,048
Allocation-block size	4 KiB	2 KiB
Allocation blocks	2,048	512
Directory entries	512	256
Tracks	1,024	128
SPT / BSH / BLM	64 / 5 / 31	64 / 4 / 15
EXM / DSM / DRM	1 / 2047 / 511	0 / 511 / 255
AL0 / AL1	F0h / 0	F0h / 0
CKS / OFF	0 / 0	0 / 0

CKS is zero because the card is treated as fixed media. CP/M's check vector is for detecting a changed disk on removable floppy drives. TEC-OS instead uses the DPH scratch words to retain directory state across warm boot. Their changed flag and scan mark determine the allocation-vector rebuild (src/cpm/bdosfile.asm:19-107). Cold-boot vector placement is explained under Allocation vectors below the workspace.

From a record to a card block

SETTRK, SETSEC and SETDMA save their arguments from BC. HOME sets track zero and SECTRAN returns the sector unchanged. No head moves and no skew table alters the sector (src/bios.asm:1-51).

MAPREC first bounds the sector to 0–63 and the track to 0–1,023. It computes record = track × 64 + sector. The low two record bits become BLKSLOT, the quarter within the SD block. Dividing the record by four gives BLKOFF, the block offset within the volume. That offset must be less than the length in DRVTAB. Adding the volume's start in 32 bits produces SDLBA. A rejected mapping leaves SDLBA unchanged, though intermediate BLKSLOT or BLKOFF values may have been stored (src/bios.asm:128-189).

Track 2 and sector 5 give record 133. Division by four gives block offset 33 and slot 1. On a volume starting at block 2,048, this is card block 2,081. Slot 1 occupies bytes 128–255 of that block (src/bios.asm:141-155, src/cache.asm:370-378).

READ masks interrupts, maps the record and calls CREAD to copy its 128 bytes from a cache line to the DMA address. It restores the preceding interrupt state and returns A = 0 for success or 1 for error (src/bios.asm:387-399, src/bios.asm:373-446, src/cache.asm:360-417).

Merging a write

Writing a quarter-block must preserve the other three quarters unless they belong to a newly allocated block. The BDOS supplies that information in C: type 0 is data, type 1 is directory and type 2 is the first write to a newly allocated allocation block. WRITE stores the type in CWTYPE and maps the record. A read-only drive then returns BIOS error 1 before changing directory marks or cached data. Mapping and type workspace may already have changed (src/bios.asm:219-237).

The BDOS applies its own R/O check before a file write. Close, function 16, has a separate read-only return: it succeeds without writing. This also holds for a file control block (FCB) that was never opened, as the source test asserts (src/cpm/bdoslog.asm:732-749, src/cpm/bdosfile.asm:209-258, src/cpm/bdosfile.asm:347-366, src/cpm/bdosfile.asm:516-530, src/cpm/bdosrec.asm:61-74, src/cpm/bdosrec.asm:274-285, test/cpm22.test.mjs:174-185). A caller using the BIOS directly can instead receive the BIOS read-only error.

Directory marking depends on the mapped block address, not merely write type 1. The first thirty-two SD blocks of G8M or sixteen of G1M are the directory. A write there sets the DPH word at offset 4 to 1. It raises the word at offset 6 to at least (BLKOFF + 1) × 16, covering all sixteen directory entries in that block. The next warm reset marks a logged-in changed drive for rebuilding through that mark at its next selection (src/bios.asm:239-287, src/cpm/bdosfile.asm:61-107).

Every write merges through CWRBH into the block's cache line. A normal miss first reads the card block so its other records survive. For type 2, WRITE selects no pre-read. CWRBH clears the whole line to zero even if it was already a cache hit then copies the record into it (src/bios.asm:298-358, src/cache.asm:419-470).

The following SD block can also be cleared without reading when it is in the same allocation block. GETKEY records the cleared block's drive and offset in BUFDRV and BUFBLK with BUFOK = 2. WRITE requires that key to name the immediately preceding block on the same drive. It also rejects the optimisation at the start of an allocation block (src/bios.asm:191-208, src/bios.asm:305-330).

A write which preserves a line's bytes keeps this key only when it names the key's own block and drive. Otherwise it clears BUFOK. With the BDOS's correct write types, out-of-order writes therefore cannot use a stale sequential key to clear an already filled block (src/cache.asm:469-511). This protection relies on the type-2 contract. A direct BIOS caller must not label existing data as newly allocated.

Every directory write, type 1, writes every changed or kept data line first, on any drive. Only after those writes succeed does its own merged line reach the card; a failed data write refuses the directory write. A data write off the logged drive sets bit 5 of CWTYPE and leaves one pending block in CPEND. Data on the logged drive may remain in several dirty lines until a console read, directory write or another flush point (src/bios.asm:343-358, src/cache.asm:496-622). Chapter 19 explains these two rules and the failure paths in full.

Sequential writes to a new file can therefore avoid data pre-reads. On a drive not logged they also avoid writing each SD block after each of its four records: one block stays pending and is written when the write moves on or a flush point arrives. On the logged drive several changed blocks can wait together until the next key read or directory write (src/cache.asm:496-622). On the starter card SAVE 8 X.COM writes sixteen records in four data blocks on A. It causes four data-block writes plus two directory-block writes, six writes in total. No reads are needed because the directory block is already cached after boot. An uncached directory can add metadata reads to a new-file operation.

Volume services and publication

The shell's CD changes drives through the numbered ROM service interface. It calls ABICALL at C008h with the service number in C (src/abi.asm:9-14, src/abi.inc:27-29, src/abi.inc:139-169, drivers/shellcd.asm:110-117). These three services expose the container:

Service	Arguments and effect
9, MOUNT	B = drive 0–3, E = container index. Mount that volume on the drive.
10, UNMNT	B = drive 1–3. Empty B, C or D.
11, DESC	E = index, HL = 32-byte destination. Copy the descriptor and substitute the current drive byte or FFh for unmounted.

VSMNT, VSUNM and VSDSC begin with VSIN. It copies the drive argument into C and invalidates MNTCB so a table read starts afresh. Normal service completion returns A = 0 with carry clear. Rejection returns TNEBAD, 1, with carry set (src/volsvc.asm:167-198, src/volsvc.asm:312-357).

A mount rejects a drive past D, an index past the table, an already mounted volume or an allocation-vector slot too small for the payload. The already-mounted check also rejects mounting a volume again on its current drive. Descriptor reads can fail too. A payload of 4,096 SD blocks or more needs a 256-byte slot. A smaller payload needs at least the 64-byte slot. The supported geometries therefore require the G8M or G1M slot respectively (src/volsvc.asm:211-265, src/volsvc.asm:426-460). An unmount rejects A and drives past D. A describe rejects an invalid index or failed table read (src/volsvc.asm:182-198, src/volsvc.asm:275-282).

Appendix B gives the register contracts. Each service has a 24-byte stack bound below its return address, including the dispatcher. test/storage-boundaries.test.mjs:205-250 contains the six-dirty-line and all-dirty-line assertions for this bound. These source assertions have not been rerun here (src/abi.inc:35-56, src/abi.inc:139-169).

Before a mount or unmount publishes a different drive assignment, VFLUSH calls CFLUSH, with no line excluded, with interrupts masked and restores their preceding state afterwards. It preserves the requested drive, index and descriptor across that call. CFLUSH attempts every dirty line. It keeps a failed line dirty for the next flush and continues with the rest, then returns failure if any write failed (src/volsvc.asm:360-389, src/cache.asm:256-301).

Validation or this flush failure leaves the drive assignment unchanged. It does not roll back card writes. Even a descriptor read can require a dirty victim write. The old assignment is the protected state at this boundary, not every byte of storage or workspace (src/vol.asm:399-416, src/volsvc.asm:211-244, src/volsvc.asm:275-322).

After a successful flush, mount changes the descriptor copy's drive field, clears the old drive entry, installs the new entry and DPH through MNONE and records index plus one in DRVIDX. Unmount simply clears the old entry. Both clear the sequential no-pre-read key and call BDOS function 37 to reset that drive. Its next use then logs it in from its directory (src/volsvc.asm:231-244, src/volsvc.asm:275-310, src/volsvc.asm:397-413).

Mounting onto the default drive also calls function 14 to select it again. Functions 27 and 31 then refer to the new volume's allocation vector and DPB. This reselection follows publication so a subsequent directory-read error uses ordinary BDOS error handling rather than the earlier validation rollback boundary (src/volsvc.asm:335-345, src/cpm/bdosfile.asm:109-146, src/cpm/bdoscon.asm:23-74). These BDOS calls use its private stack. Programs must call mount and unmount from outside an ongoing BDOS call (src/abi.inc:47-49).

The services leave the container header's drive assignments unchanged. Their flush can write pending data but their new assignment is held in RAM. A recognised reset can retain it. Power-on, an unrecognised reset or failed reselection restores the card's defaults through the boot mount path (src/boot.asm:1-6, src/boot.asm:97-104, src/volsvc.asm:13-129, src/volsvc.asm:231-244).

The starter card is format 1.1 with drives = 4, so cold boot allocates four 256-byte slots and any of its volumes fits any drive (src/boot.asm:525-633). CD ? lists the card's descriptors through service 11, CD D:GAMES mounts GAMES on the empty D through service 9, and CD C:WORK is refused because WORK is on B (drivers/shellcd.asm:99-117):

TEC-OS 0.1 for TEC-1G
A: SYSTEM
B: WORK
C: PROJECTS

A>SHELL.SVC

A:SYSTEM>GLCD.SVC

A:SYSTEM>CD ?

SYSTEM      A:
WORK        B:
PROJECTS    C:
GAMES
SPARE
A:SYSTEM>CD D:GAMES
D:GAMES
A:SYSTEM>CD C:WORK
WORK is on B:

A:SYSTEM>

The four slots use 1,024 bytes where a card with a G1M slot on A and a G8M slot on B uses 320, so the starter card's transient program area (TPA) is 46,569 bytes, 704 less than the 47,273 of such a two-volume card. A format 1.0 card reserves slots only for the drives mounted at cold boot, and a mount there must fit them: a G8M volume onto a G1M-sized slot is refused.