Solid State Drive is just like one big USB key, but without a USB controller. Below its surface Solid State Disk hides many NAND chips that are capable of storing your data.
There aren't any heads of rotating mechanisms, just many TSOP chips on one or more PCBs. We took a picture of a BitMicro SSD with SCSI interface and you can clearly see 32 chips on a PCB; and probably this is not the only PCB, as this marchitecture supports more than one PCB.
More chips means more memory, but currently we are talking about 10USB per GB, which is not that affordable.