The "spider" modification performed on Issue 1 and Issue 2 Spectrums was later incorporated into the Spectrum PCB starting with Issue 3.
The ZX Spectrum contains either one or two banks of DRAMs. The lower bank of eight 16Kbit DRAMs is present in all Spectrums, and shared between the ULA and CPU as it contains the machine's video memory. A second bank of eight DRAMs for the upper 32K may be present for a total of 48K of RAM. External 32K RAM packs were sold for those not wanting to upgrade their 16K Spectrums to 48K internally.
For an internally fitted 32K bank
, faulty 64K DRAMs were initially used. All eight DRAMs must be faulty within only one half of their storage. A link is present on the Spectrum PCB to specify which half of each of the faulty DRAMs is usable, but as this single link applies to all eight DRAMs, faults must only be present within the same half of each of them.
=== Issue 1 ===