Macintosh Classic Memory Upgrade Guide
The Macintosh Classic has 1 MB of RAM soldered to the logic board and no SIMM sockets of its own. All expansion goes through Apple's optional memory expansion board, which carries a further 1 MB of soldered RAM plus one pair of SIMM connectors. The maximum is 4 MB.[1]
Memory specifications
[edit | edit source]- On board: 1 MB soldered, not removable.[1]
- Expansion board: 1 MB soldered plus two 30-pin SIMM sockets and a configuration jumper.[1]
- SIMM speed: 120 ns or faster, in Apple's words "You must use 120-ns (or faster) SIMMs".[1]
- SIMM sizes: 256 KB or 1 MB, fitted as a matched pair.[1]
- Eight-chip modules only. Apple states that 1 MB SIMMs with fewer than eight chips will not work in the Macintosh Classic.[1]
- Maximum: 4 MB, expandable no further.[1]
Supported configurations
[edit | edit source]| Total RAM | Expansion board | SIMMs | Jumper |
|---|---|---|---|
| 1 MB | not fitted | — | — |
| 2 MB | fitted | none | "No SIMMs" position |
| 2.5 MB | fitted | 2 × 256 KB | "With SIMMs" position |
| 4 MB | fitted | 2 × 1 MB | "With SIMMs" position |
Tools
[edit | edit source]- Long T15 Torx screwdriver (at least 150 mm / 6 in) — two of the case screws sit deep in the handle recess
- Case separator or plastic spudger
- Anti-static wriststrap
- A matched pair of 30-pin SIMMs
See Recommended Tools.
Procedure
[edit | edit source]1. Prepare. Power off, unplug, work on a grounded surface.
2. Open the case. The Classic contains a CRT. Read CRT Discharge Procedure first, discharge the CRT before disconnecting anything, and do not fit a grounding wriststrap until after it has been discharged.[1]
3. Free the expansion board. Apple's instruction is to slide the memory expansion board upwards to release it from the logic board and the chassis.[1]
4. Fit the SIMMs into the pair of sockets on the expansion board, as a matched pair, with the notch matched to the socket keying.
5. Set the jumper — "No SIMMs" if the board is being installed bare, "With SIMMs" if a pair has been fitted.[1]
6. Refit the expansion board onto the logic board and reassemble.
7. Verify the total in "About This Macintosh".
Common problems
[edit | edit source]| Symptom | Likely cause | Action |
|---|---|---|
| Sad Mac, or Sad Mac with black vertical lines and a screeching sound | Jumper set wrongly for the SIMMs actually fitted | Apple's own chart puts the jumper first: verify "SIMMs" / "No SIMMs"[1] |
| Sad Mac on a 4 MB machine | 1 MB SIMMs with fewer than eight chips | Fit eight-chip modules; Apple states fewer-chip 1 MB SIMMs will not work[1] |
| Memory figure not as expected | Mismatched pair, or a module not fully seated | Use two identical modules, reseat both |
| Random instability | A failing module | Substitute known-good modules |
Sad Mac codes are decoded on Sad Mac Error Codes and with the Sad Mac Decoder.
Why 4 MB is the ceiling
[edit | edit source]The Classic is a 24-bit-addressing 68000 machine with a fixed memory decode and a ROM that probes only as far as its supported maximum; there is no hardware modification that lifts the limit. If you need more than 4 MB in a compact Macintosh, the Macintosh SE/30 is the machine that provides it.
Related pages
[edit | edit source]- Macintosh Classic
- Macintosh Classic / Classic II General Maintenance
- Macintosh Classic / Classic II Troubleshooting
- Apple Service Source