MB03+ Slim  is a powerful, compact, next-generation ZX Spectrum interface that provides the functionality of a large number of hardware and system add-ons for the ZX Spectrum and compatible computers, in an all-in-one solution. The MB03+ is normally connected to the standard edge connector of any ZX Spectrum. It consists of modern circuitry with a fast FPGA chip and is compatible with the popular divMMC/SD interface. 

Specifications :

• square shape 8x8cm board, connected to ZX edge socket in horizontal position
• powered by ZX Spectrum - very efficient switch power supply
• fully compatible with all original ZX Spectrum models
• digital video and audio output to modern TVs or PC monitors, scan line display effects possible to mimic old good retro TV/CRT displays
• FPGA - RetroCoreX board: Xilinx Artix7 - XC7A100T, the main brain of the machine
• 4MBytes SRAM + 2MBytes SRAM + 1MBytes FLASH + FRAM 8KB (system info, bios config);  RAM is expandable through expansion sockets
• batteryless RealTimeClock (RTC72421)  for esxDOS SYS driver, synchronized by internet
• Wi-Fi module ESP8266, UART connection
• 3x USB-C ports, one for a PC-link, second for PC keyboard or HUB and third for mouse (real USB HID devices)
• Custom ROMs of 16KB and 64KB (DerbyPro), diagnostic and test ROMs, possibility to use patched ROMs, e.g. 64char ROM
• tremendous sound capabilities: 3xAY/YM, TurboSound or TurboSound FM (2xYM2203), SAA1099, SounDrive/Stereo Covox/Specdrum, SID (C64) and General Sound (28 MHz Z80-CPU, 16KB ROM, 2MB RAM, 4x 8bit channels)
• Z80 DMA and FastDMA, SafeNMI, SaveINT, I/O port-based LIFO stack and other internal hardware enhancements
• Ultimate firmware - a quick boot and SetUp with easy hardware settings and switchable configurations
• divSD, divMMC, Z-Controller SD, esxDOS (UnoDOS) compatible
• TRDOS emulation via esxDOS, compatible with other systems like divide+ (G+DOS) 
• TIMEX Hi-Color and Hi-Res graphics modes and ZX-Uno's Radastan graphics, ULAplus and TrueColour palettes
• two VideoRAMs also on 48K Spectrums, three levels of non-flickering GigaScreen, Klayer mode with a transparence colour
• attribute-based 512*192 HiResColour and HiResindeXedColour modes
• HGFX - ZX Planar, HAM and FILL modes, resolutions: 256*192, 512*192, 512*384 and 720*546, up to 256 colours from 16777216

Basic comparation to MB03+ Ultimate:
- modern USB support, more USB slots
  Ultimate: has only 1 USB slot and supports only old usb devices with ps/2 protocol
- i2c for addons via qwiic cable
  Ultimate: doesn't have it.
- swap-able RetroCoreX board
  Utimate: universal internal expansion connectors, FPGA is not upgradable
- ram: 4MB SRAM, 2MB GS, 1MB FLASH, but RAM is expandable
  Ultimate: 16MB SRAM, 2MB GS, 1MB FLASH
- no internal Matrix LED
- no battery for RTC
- no CF slot, no divIDE and no BSDOS
- no internal expansions