Comparison between different ways to work with RAM in a FPGA design

•  Using D-F/Fs real expensive (400 CLBs = 800 F/F) => You may implement 100 bytes of RAM

•  LUT by nature 16x1bit RAM (400 CLBs = 800 LUTs) => You may implement 1600 bytes of RAM

•  Block RAMs "real" memory implemented in most FPGAs  16kbit/BRAM typically

•  External RAM a must for designs which uses Soft/Hard CPUs like Microblaze and PowerPC