# Number of transistors in the C64

How many transistors are there approximately in the C64 if we consider every chip on it? I think that it is something around 50.000 but I'm not sure.

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Logic

• 6510: ~3500
• VIC II: ? (est. 5000)
• 2x CIA: ? (est. 2000)
• PLA: ? (est. 1000)
• SID: ? (est. 2000)
• commodity chips: ~500?

Memory

• 64K DRAM: ~526000 (one transistor per bit, one transistor per row per bus width)
• 512 B SRAM: ~25000 (six transistors per bit
• 20K ROM: ~160000 (one transistor or diode per bit)

The bulk number goes to the RAM, 50,000 isn't nearly enough though. I've tried to (very roughly) estimate the unknown ones - I'm definitely no expert - leading to some 100,000.

edit: very embarrassing - I counted bytes as bits...So, we've got around 14,000 for logic and some 710,000 for memory.

• I'm not sure, but I think your estimates for RAM, ROM, and SRAM are low. Would there not be at least one transistor per bit? You have only accounted for one per byte. So off the top of my head I'd multiply each of these estimates by eight. Aug 20 '17 at 18:34
• @RichF: Mask-programmed ROM doesn't need a transistor per bit; a diode will suffice. Aug 20 '17 at 18:42
• @HenningMakholm Okay, that makes sense. Since ROMs were 8-bit devices, then one transistor-driven gate for the 8 diode bits per byte seems workable. The RAMs, though, were likely organized as 64k x 1bit or 16k x 4bit, either requiring 8 chips total. If somehow diode+capacitor magic could be used for the bits of the 4-bit devices, Zac's RAM estimate would still be off by a factor of two in that configuration. (Just checked, most C64s used the 16kx4bit config. Late models used 64kx4bit, requiring only two RAM chips.) Aug 20 '17 at 18:57
• @HenningMakholm The original C64 used eight 64kx1 chips (4164), the last models two 64kx4 chips (41464?). Aug 20 '17 at 19:43
• The PLA was apparently implemented in a variety of different chips at different times, but they were mostly similar to the original 82S100, which has 16 inputs, each of which is carried in both input form and inverted (requiring at least 16 transistors) into a grid of transistors joining those 32 input lines with 48 "product term" lines that then feed into a bunch of OR gates at the 8 outputs (which must require at least one transistor per product line per output line), so by my count these chips had at least 1,936 transistors. Aug 22 '17 at 22:35