This model is almost same with 5551-R.
CPU is degraded to i486SX-33. The most distinctive feature of 5521 is that a Cirrus GD5428 1MB SVGA /A was given for YSB and YWB models instead of PS/55 Japanese Display Adapter.
Modified R/L planar
is used for this model (QFP IBM486DL2-66 is omitted from U1). 486SX33 sits on a
Socket 1 at U2. This planar has a jumper block at the location of
J6 on R /L planar. According to quick reference
the jumper should be turned on when a double-clock processor option is used
instead of a stock 486SX33 CPU.
Cirrus GD5428 SVGA /A (adapter ID: 917A)
Cirrus GD5428 SVGA /A (1MB VRAM standard but upgradeable to 2MB) was not available as an "optional part". It's different from Cirrus SVGA used in Server 500 and is free from "flicker disease". There are solder pads for additional VRAM and the circuit is ready for adding SOJ VRAM's. Win95 built-in driver can use full 2MB but NT4 detects only 1MB.
Go HERE for more information about the Cirrus SVGA adapter.